Download
1 / 20
E N D
How Earthquakes Occur • An earthquake occurs when rocks break and slip along a fault in the earth. Energy is released during an earthquake in several forms, including as movement along the fault, as heat, and as seismic waves that radiate out from the "source" and causes the ground to shake, sometimes hundreds of kilometres away.
The Three Main Types of Waves • P WAVES – cause rock to move back and forth • S WAVES – shakes the earth up and down • L WAVES – move side to side • R WAVES – cause surface material to move in vertical circles
Where They Occur • Wherever thetectonic plates that make up the Earth's crust subduct, crumple, or grind past each other, earthquakes occur. Earthquakes occur all over the world; however, most occur on active faults. 90% of the world's earthquakes occur along these plate boundaries. The "Ring of Fire" circling the Pacific Ocean, and including Canada's west coast, is one of the most active areas in the world. • Mountains are built by tectonic and volcanic activity. Everywhere in the world where these activities happen, earthquakes occur with them. Besides North America, two large regions in particular are at high risk: • The Pacific Rim • The Mediterranean and Middle East regions • • Divergent boundaries: • Along sides of rift valley • Indicate horizontal extension • Transform boundaries: • Shallow focus • Convergent boundaries: • Collision boundaries between continents • Subduction
Seismographs • Seismographs are instruments used to measure earthquake waves. • A seismogram is the record they produce of the arrival times and magnitude of earthquake waves. • Modern seismometers amplify the wave motion electronically and can detect even very weak or very distant signals. • Seismographs enable us to measure the size of earthquakes and to locate them accurately.
The Damage Earthquakes Create • Earthquake damage depends on what area is hit. If an unpopulated region is struck, there will be low loss of life or property. If it hits a large city, there may be many injuries and destruction. Many of the areas at risk on the Ring of Fire are largely populated. Major earthquakes hitting those areas today could produce terrible damage. • Earthquakes have the power to uproot trees and send them crashing into buildings. They can trigger landslides and avalanches, and cause flooding and tsunamis. Human structures are also at risk. Buildings with thick, heavy walls do not resist shock waves very well. Violent earthquakes often cause structures to collapse, burying people underneath. Brick buildings are the most vulnerable. Chimneys and heavy roof tiles are often shaken off during the tremors, and can crash into bystanders or people passing by. The shaking of the earth is sometimes not the greatest disaster. It is in the ensuing fires and floods that often the greatest damage occurs.
Preparing For An Earthquake • In those parts where strong earthquakes may occur people build their houses upon firm ground. Only the most elastic materials should be used, like wood and reinforced concrete instead of brick or stone. They would try to avoid overloading the higher parts of the building and do everything possible to keep the center of gravity of the whole low. Brick chimneys on the rooftops tend to fall off at an intensity of VI. • People that live in third world countries are usually the ones who have the most damage after an earthquake, because their houses are not strong enough to withstand an earthquake. People living in the first world countries are less vulnerable to the dangers of an earthquake because their houses are better built.
Effects of Earthquakes • Ground motion • Fires • Landslides • Liquefaction • Aftershocks • Tsunamis Fire Liquefaction Tsunami
The 5 Tips In a case of an earthquake… • You should get under dining tables or anything that can support a lot of weight. Cover your neck and face so that it’s better protected from falling objects and broken glass. If possible, face away from any glass. Hold onto the table or desk because most likely it will move, so be prepared to move with it. Hold that position until the shaking stops. If a table or desk is not available, you should stand in the doorway. • Medical aid, water, transportation, electricity, and communication may be unavailable or severely restricted for several days or weeks after a large earthquake. You should be prepared to take care of yourself for at least three days. • In the case of an earthquake, do not run outside or use staircases or elevators. • If you are driving during an earthquake, you should move to the shoulder. Stay away from overpasses, bridges, large buildings, and power lines. Stay in your car until the shaking stops. • The most important thing of all is to stay calm.
The Richter Scale M=1 to 3: Recorded on local seismographs, but generally not felt M=3 to 4: Often felt, no damage M=5: Felt widely, slight damage near epicentre M=6: Damage to poorly constructed buildings and other structures within 10's km M=7: "Major" earthquake, causes serious damage up to ~100 km (recent Taiwan, Turkey, Kobe, Japan, and California earthquakes). M=8: "Great" earthquake, great destruction, loss of life over several 100 km (1906 San Francisco, 1949 Queen Charlotte Islands). M=9: Rare great earthquake, major damage over a large region over 1000 km (Chile 1960, Alaska 1964, and west coast of British Columbia. Modified Mercalli Intensity Scale (I) - Not felt except by a very few under especially favourable conditions. (II) - Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing. (III) - Felt quite noticeably by persons indoors, especially on the upper floors of buildings. Many do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a truck. Duration estimated. (IV) - Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. (V) - Felt by nearly everyone; many awakened. Some dishes and windows broken. Unstable objects overturned. Pendulum clocks may stop. (VI) - Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken... books off shelves... some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight. (VII) - Difficult to stand... furniture broken..damage negligible in building of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving motor cars. (VIII) - Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture moved. (IX) - General panic... damage considerable in specially designed structures, well designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. (X) - Some well built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent." (XI) - Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly. (XII) - Damage total. Lines of sight and level distorted. Objects thrown into the air. The Measurement of Earthquakes
The Mexico Earthquake Article Natural Hazards Slides Vol. 2 - Earthquake Events: Earthquake of 9/19/1985, Mexico City EARTHQUAKE OF SEPTEMBER 19, 1985 MEXICO CITY, MEXICO On September 19, 1985, at 7:17 A.M., a Richter magnitude 8.1 earthquake occurred on the Pacific coast of Mexico. The damage was concentrated in a 25 km2 area of Mexico City, 350 km from the epicenter. Of a population of 18 million, an estimated 10,000 people were killed, and 50,000 were injured. In addition, 250,000 people lost their homes, and property damage amounted to $5 billion. Over 800 buildings crumbled, including hotels, hospitals, schools, and businesses. Communications between the Mexican capitol and the outside world were interrupted for many days. Surrounding areas affected by the earthquake included the Mexican States of Jalisco, Guerrero, and Michoacan. Damage in the epicentral area was restricted to a few tourist resorts and industrial estates along the Mexico Pacific coast. A two-meter tsunami also caused some damage in this area. There are geologic reasons why Mexico and especially Mexico City are vulnerable to earthquake damage. Along the west coast of southern Mexico and Central America the Cocos Plate dips beneath the North American Plate producing a very active seismic zone. Since the beginning of the twentieth century 35 earthquakes of magnitude greater than 7.0 have occurred in this zone. The location of the 1985 earthquake's epicenter near the coast at the border between the states of Michoacan and Guerrero was not a surprise. Prior to the 1985 earthquake this area, located between two areas that had experienced recent earthquakes, was known as the "Michoacan Gap." The "gap" was filled in 1985 by the main shock and a severe aftershock (magnitude 7.5) that occurred the next day. Mexico City itself lies in a broad basin formed approximately 30 million years ago by faulting of an uplifted plateau. Volcanic activity closed the basin and resulted in the formation of Lake Texcoco. The Aztecs chose an island in this lake as an easily defended location for their capitol. The expansion of the capitol (Mexico City) and the gradual draining of the lake left the world's largest population center located largely on unconsolidated lake-bed sediments. These soft sedimentary clay deposits amplified the seismic waves, or they subsided carrying buildings down with them. Double resonance coupling between the earthquake waves, the subsoils, and the buildings caused intensity IX shaking in some areas, lasting up to three minutes. Earthquakes in 1957 and in 1979 also damaged Mexico City. However, neither of these earthquakes was quite as devastating as the 1985 earthquake. In the area of greatest damage in downtown Mexico City, some types of structures failed more frequently than others. In the highest damage category were buildings with six or more floors. Resonance frequencies of these buildings were similar to the resonance frequencies of the subsoil. Because of the "inverted pendulum effect" and unusual flexibility of Mexico City structures, upper floors swayed as much as one meter and frequently collapsed. Differential movements of adjacent buildings also resulted in damage. A flexible building often failed if it was held by adjacent, more rigid lower buildings. Damage or failure often occurred where two swaying buildings came in contact. Corner buildings were also vulnerable to damage. Lessons learned from the patterns of earthquake damage need to be quickly applied to prevent another disaster when an earthquake releases stress that is building in another area--along the Mexican coast between Acapulco and Zihuatanejo.
The Kobe Earthquake Article Natural Hazards Slides Vol. 2 - Earthquake Events: Kobe Earthquake KOBE The Earthquake At 5:46 A.M. local time on January 17, 1995, a major earthquake occurred near the City of Kobe, Japan. The 6.9 magnitude earthquake had 40 km of bilateral rupture from a hypocenter 10 km under the northern tip of the island of Awaji in the Sea of Japan. The greatest intensity of shaking was in a narrow corridor of two to four kilometers stretching 40 km along the coast of Osaka Bay. The ground moved as much as five meters in some places. The worst destruction ran along the previously undetected fault on the coast, east of Kobe. Kobe's major business, industrial and port facilities, and residences are located in this strip. Note: This earthquake is also called the Hyogo-Ken Nambu, Japan, Earthquake and Southern Hyogo Prefecture Earthquake. The DamageThe earthquake caused extensive damage to the coastal cities that border Osaka Bay and to the northern portion of Awaji Island. Inland cities located near the northern end of the fault rupture sustained significant damage. Osaka (Japan's second largest city), Kyoto, and Shiga, farther to the northeast, reported extensive damage from the quake. The earthquake caused 5,480 deaths*the highest death toll in Japan since the Great Kanto Earthquake of 1923 (142,000 deaths). About 94,900 people were injured; nearly 317,000 people moved to evacuation centers. Buildings:More than 192,700 houses and buildings were totally destroyed by the earthquake. Most of the damaged buildings were unsafe to occupy and had to be torn down later. The repair costs to buildings were estimated at more than $100 billion (U.S. Dollars). The design code in effect at the time of the construction was a major factor in determining the extent of damage to the commercial and residential buildings. Modern high-rise buildings typically fared better than older residential construction. Transportation:Kobe is located within the main transportation corridor between central and southern Honshu. The Hanshin Expressway, supported by large hammerhead reinforced concrete piers, failed over a twenty kilometer length. The supporting steel girders of the Wangan Expressway (along the harbor shore) were dislodged from their seats, although few collapsed. Rail facilities were particularly hard hit. All three main lines through the corridor sustained embankment failures, overpass collapses, distorted rails, and other severe damage. The elevated viaduct that carries the Bullet Train was severely damaged when supporting columns underwent shear failure. There was damage to the subway systems, including a rare instance of severe earthquake damage to a modern tunnel for reasons other than fault displacement near the portal. Rail and road transportation disruption affected a number of companies relying on rapid production systems. Due to effects on transportation, automobile and motorcycle manufacturers temporarily shut down factories located far from the earthquake site. Port Damage:The port of Kobe, one of the largest container facilities in the world, sustained major damage. Shipping had to be diverted to other ports. Cessation of port functions impeded the shipment of raw materials and parts between businesses in Japan and their subsidiaries or partners overseas. This impacted the electronics, apparel, and auto manufacturing industries. There was severe and widespread liquefaction as a result of the earthquake. Lateral ground deformation caused the piers of the highway bridge and electric rail bridge between Port Island and Kobe to lean between two and three degrees toward the waterfront. Of 186 heavy shipping berths, 179 were inoperable after the earthquake. Utilities:Electric power and telecommunications services were not disrupted, but most of Kobe lost essential services such as water, water treatment, and gas utilities. Electrical power performed well with very little reduction in service during the earthquake, and was completely restored within one week. Underground water pipelines sustained severe damage in the earthquake. Numerous breaks resulted in a general lack of service in Kobe, Ashiya, and Nishinomiya. Water was restored within two weeks and gas was restored within a month. Fires:Almost 150 fires started, most within minutes of the earthquake, and primarily in densely built-up low rise areas of the city. The fires destroyed one million square meters of residential area in Kobe.
Kobe and Mexico City Earthquakes • The Kobe earthquake of magnitude 7.2 struck the region of Kobe and Osaka in south-central Japan. This region is Japan’s second-most populated and industrialized area, after Tokyo. The shock occurred at a shallow depth on a fault running from Awaji Island through the city of Kobe, which in itself has a population of about 1.5 million. A powerful Mexico City earthquake registering magnitude of 8.1 rocked central Mexico. The quake was centered in the coastal mountains of the Michoacan Province and caused substantial damage throughout central Mexico, including in Mexico City - some 240 miles east of the epicentre. • The Kobe earthquake struck on Tuesday, January 17th 1995, at 5:46 a.m. local time. The Mexico City earthquake struck at 7:17 a.m. September 19th, 1985. • Damage was recorded over a 100-kilometer radius from the epicentre, including the cities of Kobe, Osaka, and Kyoto, but Kobe and its immediate region were the areas most severely affected. Damage was particularly severe in central Kobe, in an area roughly 5 kilometres by 20 kilometres parallel to the Port of Kobe. This coastal area is composed primarily of soft alluvial soils and artificial fills. Severe damage extended well northeast and east of Kobe into the outskirts of Osaka and its port. Severe damage occurred to about 500 buildings in Mexico City with widespread light to moderate damage in other parts of the country. Although quake killed over 8,000 people, causalities would nave been much higher if the quake had occurred just a couple hours later when the schools and office buildings would have been full with people.
Japan is known to have a lot of minor and a few major earthquakes. Mexico City has been rocked several times in the past. It is largely built upon soft, poorly consolidated lake sediments from the former Lake Texcoco, which was drained by the Spanish following their occupation of the region. Thick sequences of soft sediments like these tend to amplify seismic waves and cause the ground to shake much more vigorously than the surrounding bedrock. • The Kobe earthquake lasted about twenty seconds. The Mexico City earthquake was about three minutes long, but to a lot of people it seemed like an eternity. • People did not have any warning for either of the two earthquakes. • Nearly 5,500 deaths have been confirmed, with the number of injured people reaching about 35,000. Nearly 180,000 buildings were badly damaged or destroyed, and officials estimate that more than 300,000 people were homeless on the night of the earthquake. In the Mexico City quake, at least 9,500 people were killed, about 30,000 were injured, more than 100,000 people were left homeless, and severe damage was caused in parts of Mexico City and in several states of central Mexico. The death toll from this earthquake may be as high as 35,000. It is estimated that the quake seriously affected an area of approximately 825,000 square kilometres, caused between 3 and 4 billion U.S. dollars of damage, and was felt by almost 20 million people.
Kobe’s current estimates of the repair costs in the earthquake have been reported in the range of $95 billion to U.S.$147 billion, many times the damage inflicted by the 1994 Northridge Earthquake. These figures do not include the loss to building contents such as equipment and inventory, which will also be substantial. Mexico City got help from the states of the (Mexican) Republic and from people and institutes from abroad did not have to be waited for. The assistance was immediate. Aid and relief brigades came from Germany, Belgium, Algeria, Brazil, Canada, Colombia, Costa Rica, Cuba, Spain, the United States, France, Great Britain, the Netherlands, Israel, Panama, Switzerland, Venezuela, etc. Between September 19, 1985 and January 5, 1986, assistance reached the country, with 296 flights originating from 45 different countries. A figure that does not include the countries that made donations exclusively in cash. Aid by land came from 6 countries.
Bibliography • Encyclopedia of Earthquakes and Volcanoes, 2001. New Edition. • http://earthquake.usgs.gov/recenteqsww/world_merc.html\ • http://pubs.usgs.gov/gip/earthq1/ • http://www.crustal.ucsb.edu/ics/understanding/ • http://www.pgc.nrcan.gc.ca/seismo/eqinfo/q-a.htm • http://www.seismo.unr.edu/ftp/pub/louie/class/100/plate-tectonics.html
National Geographic. Volume 169, No.5, (May 1986): pg. 654 • National Geographic. Volume 188, No. , (July 1995): pg. 112. • Tazieff, Haroun. When The Earth Trembles. New York: Harcourt, Brace & World, Inc, 1964.
